The present invention is directed, in general, to a surface acoustic wave (SAW) identification tag and, more specifically, to an interdigital transducer on a SAW tag adapted for code discrimination and methods of operation and manufacture thereof.
A number of different types of electronic identification devices are currently being attached to objects for identification of such objects. The various kinds of devices being employed range from ubiquitous bar codes and magnetic strips to the much more sophisticated radio freqrency identification (xe2x80x9cRFIDxe2x80x9d) devices. In the case of bar codes and magnetic strips, significant limiting factors include line-of-sight reliability, tag damage and surface dirt problems, and a relatively short effective range. Magnetic strips, for example, generally require the reader to be in direct contact and properly oriented with the strip in order to detect and decode data. In those few cases where a magnetic strip is read with a device other than a direct contact reader, the effective reading range is still only a few centimeters at best. Similarly, the effective range for reliably reading bar codes is also typically no better than a few centimeters, at best. Because the range at which bar codes and magnetic strips can be read is so short, they are usually read one at a time and seldom does one bar code or magnetic strip interfere with another.
The shortcomings of bar code and magnetic strips as identification devices has caused a renewed and revived interest in various RFID tag embodiments. RFID tags can be conveniently divided, as a general rule, into chip tags and chipless tags. Chipless tags generally have about the same read range as bar codes or magnetic strips and, therefore, share a major shortcoming. Prior art RFID chip tags can be fabricated with a significantly longer reliable read range than chipless tags, magnetic strips or bar codes have, but they are generally so expensive that their use is limited to discrete applications where the expense can be economically justified. In most cases, prior art RFID chip tags are individually read and little opportunity exists for tag responses to interfere or collide with one another.
A RFID tag with a long read range that can be inexpensively fabricated has been recently developed. This RFID tag is based on surface acoustic wave (SAW) technology. A complete and detailed description of SAW identification tags 120 is set forth in detail in U.S. patent application Ser. No. 10/024,624, entitled xe2x80x9cSurface Acoustic Wave Identification Tag Having Enhanced Data Content and Methods of operation and Manufacture Thereof,xe2x80x9d Hartmann, Clinton S. (xe2x80x9cHartmann Onexe2x80x9d), commonly assigned with the invention and incorporated herein by reference. A description of SAW identification tag readers 130 to read such tags is described in detail in U.S. patent application Ser. No. 10/066,249, entitled xe2x80x9cReader For a High Information Capacity Saw Identification Tag and Method of Use Thereof,xe2x80x9d Hartmann, Clinton S. (xe2x80x9cHartmann Threexe2x80x9d), also commonly assigned with the invention and incorporated herein by reference. Because such tags are inexpensive, they can be attached to a large number of objects (such as all the objects on a shipping pallet) and because they have sufficient range to permit a tag reader to interrogate a large number of tags at the same time, the signal interference or code collision problem caused by multiple responses must be addressed as well as any inter-symbol interference problems caused by so many responses being transmitted at one time. These issues need to be resolved before the full potential of SAW identification tags can be realized.
Accordingly, what is needed in the art are systems and methods that permit a user to reliably distinguish between multiple responses to an interrogation signal that are emanating from SAW tags that are in close proximity.
To address the above-discussed deficiencies of the prior art, the present invention provides a surface acoustic wave (SAW) identification tag having a coded transducer and methods of operating and manufacturing the tag. In one embodiment the tag includes: (1) a piezoelectric substrate having a number of reflectors distributed among a group of slots arranged by both pulse position and phase position on the substrate for encoding a number by pulse and phase position; and (2) a SAW transducer located on the substrate for generating a coded interrogation pulse.
Thus the present invention provides a partial solution to a potential collision problem. When a large number of response signals are detected when a SAW tag reader sends out an interrogation pulse it is necessary to have a means to electronically identify those responses that have the highest probability of being returned by tags of interest. Where items of interest are identified by locating thereon an embodiment of a SAW identification tag as described herein, a SAW tag reader can be programmed to exclude all tags from consideration as potential candidates for identification except those tags generating a response to a transducer sending a designated coded interrogation pulse.
In one embodiment, the invention provides for the SAW transducer to generate a coded interrogation pulse using phase shift keying while in another embodiment a coded interrogation pulse is generated using frequency shift keying. In still another embodiment the SAW transducer generates a coded interrogation pulse that has the well known Barker code sequence. Those of ordinary skill in the pertinent art will recognize that any type of coding is well within the intended scope of the present invention.
In a particularly beneficial embodiment of the present invention of the SAW identification tag, the coded interrogation pulse is associated with a family of objects. Thus, a SAW identification tag using a predetermined code for an interrogation pulse will always be associated with a specific family of objects.
In still another embodiment of the invention, a SAW identification tag reader is associated with the tag. This association is a powerful anti-collision feature that permits a user to separate tags returning response signals into SAW tags of interest and SAW tags that are not of interest. This permits the SAW identification tag reader to only process reflected pulses from tags that have a predetermined coded interrogation pulse. Thus, because the SAW tag reader is not processing SAW tags that do not have a predetermined coded interrogation pulse, a more efficient and reliable object identification system can be enabled leaving more computer power to be directed to SAW tags that are of interest. In one aspect of this embodiment, the coded interrogation pulse from a specific SAW identification is identified by using code division multiplexing.
The present invention also provides embodiments for the operation and manufacture of a SAW identification tag having a coded transducer. These embodiments are hereinafter described in sufficient detail for one of ordinary skill in the pertinent art to understand
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.